Jerome,
Please find below various links that refers to how to implement PLL in Labview (the first link has a simulation example to download):
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RNAME=ViewQuestion&HOID=506500000008000000DE060000&ECategory=LabVIEW.LabVIEW+General
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RNAME=ViewQuestion&HOID=5065000000080000009A2F0000&ECategory=LabVIEW.LabVIEW+General
If you do have NI hardware,here are a few example programs from our developper zone:
http://zone.ni.com/devzone/explprog.nsf/6c163603265406328625682a006ed37d/920385efadb85bda8625681100778509?OpenDocument
http://zone.ni.com/devzone/explprog.nsf/6c163603265406328625682a006ed37d/9fc3b8ddce45bd30862568b800788320?OpenDocument
http://
zone.ni.com/devzone/explprog.nsf/6c163603265406328625682a006ed37d/35e66a955f98a26a86256a2a007418b6?OpenDocument
Regards,
Cyril Bouton
Applications Engineering
National Instruments
Cyril Bouton
Active LabVIEW Developper